From my experience MariaDB is not necessarily better than MySQL. The 8.x line brought many interesting features. I dream on switch to Postgres, and try every year but for my use case MySQL is still superior (100Bi+ rows for large texts, and heavy modified - I´m also space constrained - So I need data compression and the VACUUM are not good.)
The percona distribution is very good!
The storage engine is one of postgres's weakest points. I hope OrioleDB will eventually give us a more robust and easier to use replacement.
Is there anything in 8.0.x/8.4.x line that isn't present in MariaDb latest?
From my experience, mariadb is about the same as mysql... depending on the queries, it can either be fine, or slow as balls. I'm actually considering switching to pgsql to see if its any better. /shrug
If space constrained and wanting compression, why not do that at the filesystem or block layer if it's not supported in the app?